Motor vehicle frame structure and crashbox therefor

ABSTRACT

A crashbox is provided for connecting a bumper carrier and a longitudinal beam in a frame structure of a motor vehicle. The crashbox has a section that is compressible in a longitudinal direction and a first fixing element for attachment to the longitudinal beam and a second fixing element for attachment to the bumper carrier at opposite ends of the section. The first fixing element is in the form of a spigot member that is insertible into a cavity in the longitudinal beam and a support strut extends between two rigid side flanks of the spigot member through an internal cavity of the spigot member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/769,156, filed Apr. 28, 2010, which is a divisional of U.S. patentapplication Ser. No. 12/061,382, filed Apr. 2, 2008, and which claimspriority to German Patent Application No. 102007015865.5, filed Apr. 2,2007, which are all incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a crashbox and a motor vehicle framestructure utilizing such a crashbox.

Crashboxes are conventionally built into a motor vehicle frame structurebetween the longitudinal beams thereof and a bumper carrier in order toabsorb impact energy by the deformation thereof in the event of a nonetoo severe collision and thereby prevent the possibility of one of thelongitudinal beams being deformed. Deformation of a longitudinal beam isonly reparable, if at all, at high cost.

It is conventional for such a crashbox to have a boxlike structure withwalls that extend as an extension of the longitudinal beam and arestructured such as to be compressed in bellows-like manner in the eventof an impact, and also flanges which are aligned transversely relativeto these walls and serve for the attachment of the crashbox to a bumpercarrier and an end face of the longitudinal beam.

The construction of the frame structure could be simplified if thecrashbox could be fixed to the longitudinal beam, not with the help ofmutually opposite flanges, but rather, by sticking a spigot member ofthe crashbox into a cavity in the longitudinal beam which,conventionally, is usually in the form of a hollow square section. Inorder to effectively protect the longitudinal beam from deformation inthe event of a collision, it is necessary to introduce the forcesarising during the collision into the longitudinal beam such that theyare distributed as uniformly as possible over the cross section thereof.This is more difficult in the case of a plugged-in crashbox than it isfor one mounted in conventional manner by means of flanges since theforce-distributing and compensatory effect of the flanges no longerexists. Consequently, for the purpose of compensation, it is importantto produce a close contact between the flanks of the spigot member andthe longitudinal beam over a large surface area.

However, in order to enable the spigot member to be inserted, the crosssection thereof must be somewhat smaller than that of the cavityaccommodating it. When this is the case however, the spigot membercannot touch the opposite walls of the cavity at the same time andintroduce force into them.

In order to fulfill these contradictory demands, it is necessary toexpand the spigot member following its initial introduction into thecavity with a degree of play. Experiments have shown however, that thespread-out side flanks of the spigot member are driven towards oneanother again by the deformation occurring during a collision and tendto bend the opposing walls of the longitudinal beam to which they areattached towards each other. This must be avoided as the crashbox wouldotherwise lose its purpose.

There is therefore a need for a crashbox which can be easily andeconomically installed on the one hand but which nevertheless ensureseffective protection of the longitudinal beam from deformation on theother. In addition, other objects, desirable features andcharacteristics of the present invention will become apparent from thesubsequent detailed summary, description, abstract, and the appendedclaims, taken in conjunction with the accompanying drawings and thisbackground.

SUMMARY

In accordance with the invention, at least one object is achieved inthat, in the case of a crashbox for connecting a bumper carrier and alongitudinal beam in a frame structure of a motor vehicle whichcomprises a section that is compressible in a longitudinal direction anda first fixing element for attachment to the longitudinal beam and asecond fixing element for attachment to the bumper carrier at oppositeends of this section, wherein the first fixing element is in the form ofa spigot member that can be inserted into a cavity of the longitudinalbeam, a support strut extends between two rigid side flanks of thespigot member through an internal cavity of the spigot member. Thesupport strut limits the compliance of the spigot member in the face ofa force that is effective from the compressible section and drives theflanks of the spigot member towards each other so that a closingmovement of the flanks such as would exceed the bounds of the resilientductility of the longitudinal beam can be prevented.

In order to enable the spigot member to be introduced into the cavity ofthe longitudinal beam with a certain amount of play on the one hand butnevertheless enable the flanks thereof to come into close contact withthe walls of the longitudinal beam on the other, provision can be madeaccording to a first embodiment for the support strut to comprise atleast one section that is connected to one of the flanks and unconnectedto the respective other flank. In consequence, the support strut doesnot hinder the spreading of the flanks of the spigot member whenattaching it to the longitudinal beam. A deformation of the spigotmember by a movement of the flanks towards one another is howeverlimited by the support strut.

According to a second embodiment, the two flanks are indeed connected toone another by the support strut, but the support strut incorporates apredetermined break point in order to enable the flanks to spread apartwhen assembling the crashbox.

The support strut is preferably a web member extending in the directionin which the spigot member is inserted.

In order to provide the crashbox with a closed external shape on the onehand and yet enable the flanks thereof to spread apart on the otherhand, the spigot member preferably comprises an outer skin that isexpandable in a direction perpendicular to the side flanks

The possibility for such expansion can be created, in particular, inthat the outer skin has a corrugated shape in a section connecting thetwo side flanks

In order to provide for a simple and inexpensive manufacturing process,the outer skin is expediently joined to the compressible section inmaterial-uniting, preferably, one-piece manner.

According to a preferred embodiment which is realizable from a smallnumber of inexpensive individual parts, the side flanks each compriseone of two mutually opposite webs of an H-shaped profile, and thesupport strut is formed by a centre web member of this profile.

An exemplary embodiment also includes a frame structure for a motorvehicle comprising at least one longitudinal beam and a bumper carrierwhich is attached to the longitudinal beam by a crashbox of the typedescribed above. If the side flanks of the spigot member are attached toopposite walls of a cavity of the longitudinal beam and thereby spreadapart, a gap will exist between a section of the support strut connectedto one of the flanks and the respectively oppositely located flank or asection of the support strut connected to this flank. In the case wherethe spigot member of the crashbox originally exhibited a predeterminedbreak point, the gap is formed at the location of this predeterminedbreak point.

The attachment of the spigot member to the longitudinal beam ispreferably effected with the aid of bolts which pass through theopposite walls of the longitudinal beam and the flanks of the spigotmember.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 shows a perspective view of a part of the frame structure of amotor vehicle in accordance with the present invention;

FIG. 2 shows an enlarged sectional view of the frame structure shown inFIG. 1;

FIG. 3 shows a perspective exploded view of an end of the crashbox inaccordance with the present invention;

FIG. 4 shows a cross section through the spigot member of the crashboxwhen inserted into a longitudinal beam, prior to the attachment of thecrashbox to the longitudinal beam;

FIG. 5 shows a cross section analogous to FIG. 4 in the attached state;

FIG. 6 shows a longitudinal section through the spigot member and thetip of the longitudinal beam accommodating the spigot member in theattached state;

FIG. 7 shows a longitudinal section analogous to FIG. 6, whichrepresents the state after a collision;

FIG. 8 shows a sectional view in accordance with a modified embodimentof the invention, analogous to FIG. 4; and

FIG. 9 shows a further sectional view in accordance with a modifiedembodiment of the invention, analogous to FIG. 4.

DETAILED DESCRIPTION

The following detailed description of the invention is merely exemplaryin nature and is not intended to limit the invention or the applicationand uses of the invention. Furthermore, there is no intention to bebound by any theory presented in the preceding background of theinvention or the following detailed description of the invention.

FIG. 1 shows a perspective view of a part of the frame structure 1 of amotor vehicle chassis with longitudinal beams 2 and a bumper cross beam3. Crashboxes 4 are arranged in the form of an extension of thelongitudinal beams 2 between the bumper cross beam 3 and thelongitudinal beams 2. The bumper cross beam 3 can be the carrier of afront bumper or a rear one. The longitudinal beam 2 is substantiallytubular with a rectangular cross section and has open longitudinal endsinto which a respective spigot member of the crashbox 4 is inserted,said spigot member being hidden in FIGS. 1 and 2. The spigot member isanchored to the longitudinal beam 2 with the aid of bolts 6 which extendthrough borings in the mutually opposite side walls 7 of the beam.

FIG. 3 shows a perspective view of a part of the crashbox 4 includingthe spigot member that is to be introduced into the cavity of thelongitudinal beam 2 and is designated by 5 herein. The crashbox 4comprises a compressible main section 8 which is only partly illustratedin FIG. 3 and is substantially in the form of a tubular member having atypical length of about 20 to 25 cm and a rectangular cross section. Atan end thereof which is not illustrated in FIG. 3, the main section 8 isclosed by a plate-like flange which serves for attachment to acomplementary flange of the bumper cross beam 3. At the end thereofshown in FIG. 3, the main section 8 is extended in one-piece manner by asleeve 9, the height and width dimensions of which are somewhat smallerthan those of the main section. When the spigot member 5 is insertedinto the longitudinal beam 2, a peripheral shoulder 10 between the mainsection 8 and the sleeve 9 serves as a stop which limits the depth ofpenetration of the spigot member 5 into the longitudinal beam 2.

The sleeve 9 has a substantially horizontal upper and lower wall in eachof which a groove 11 extending in the longitudinal direction is formed.

Side walls 14 of the sleeve 9 are provided with bolt holes 12.

Corresponding bolt holes 13 are formed in two lateral webs 15 of anH-profile piece 16 which is intended to be placed inside the sleeve 9 incontact with the side walls 14 thereof. A predetermined break point 18,at which the material thickness of a web member 17 is less than that ofthe surrounding area, is formed in the central web member 17 of theprofile piece. The length of the profile piece 16 amounts, in likemanner to that of the sleeve 9, to approximately 50 mm; it consists of asolid, but brittle metal, preferably an aluminium alloy.

FIG. 4 shows a sectional view through the sleeve 9 and the profile piece16 placed therein, these together forming the spigot member 5, and alsoa view through the longitudinal beam 2 accommodating the spigot member5. The spigot member 5 is accommodated in the longitudinal beam 2 with acertain degree of play in the height and width directions. There is agap 19 of a few millimeters in width between the respective side walls 7and 14 of the longitudinal beam 2 and the sleeve 9.

In order to attach the crashbox 4 to the longitudinal beam 2, the bolts6 are pushed through the bolt holes 20 in the longitudinal beam 2 andthe bolt holes 12 in the sleeve 9 and screwed into an internal thread inthe bolt holes 13 in the profile piece 16. The tensile force of thebolts 6 that is consequently effective on the profile piece 16eventually leads to rupture of the profile piece 16 at the predeterminedbreak point 18, and the sleeve 9 is widened at the level of the grooves11 as can be seen in FIG. 5. In this way, a more intimate, snug-fittingand frictional contact between the side walls 14, 7 of the sleeve 9 andthe longitudinal beam 2 is obtained, this thereby enabling uniformintroduction of compressive forces into the longitudinal beam 2 in theevent of a collision.

In like manner to FIG. 5, FIG. 6 shows the installed spigot member 5with its ruptured predetermined break point 18, but this time in theform of a horizontal sectional view. A corresponding sectional viewafter a collision and compression of the main section 8 of the crashbox4 is shown in FIG. 7. The forces arising from the deformation of themain section 8 drive the side walls 14 of the sleeve 9 towards oneanother, but the side walls 14 can only move so far towards one another,namely, until the two fragments of the central web member 17 meettogether. As can be seen in FIG. 7, this does of course also lead to aslight deformation of the tip of the longitudinal beam 2, but thisdeformation cannot be greater than the total width of the gap 19 priorto the bolting of the crashbox 4 to the longitudinal beam 2. Thus,insofar as the width of this gap 19 is selected small enough, it can beensured that the deformation of the longitudinal beam 2 does not exceedthe elastic limit thereof. It is thus sufficient to merely loosen thebolts 6 for the longitudinal beam 2 to return to its original shape. Therepair work required to the frame structure after a none too severe acollision can therefore be restricted to the crashboxes 4 thereof andpossibly also the bumper cross beam 3.

In the illustration of FIGS. 4, 5, the predetermined break point 18occupies only a small fraction of the total width of the central webmember 17 and one might assume that, in the event of upsetting of thecrashbox 4, the two fragments of the central web member 17 wouldseparate apart in the vertical direction and thus be able to slide aboveone another, this thereby substantially negating the supporting effectof the central web member 17 in the event of a collision. However,experiments have shown that such a process of sliding above one anotherdoes not occur, but instead, the irregularly formed mutually facingedges of the fragments hook together and actually prevent such aseparating movement.

FIGS. 8 to 9 show modified embodiments of the invention each analogousto the sectional view of FIG. 4. In FIG. 8, the H-profile piece 16depicted in FIG. 4 is replaced by two T-section profiles 22 which aremutually arranged as a mirror-image, whereby the crossbar of the Tcorresponds to a respective one of the lateral webs 15 and the foot 21of the T to a respective one of the fragments of the central web member17. That is to say, the essential difference between the embodiment ofFIG. 8 and those of FIGS. 4 to 7 lies in the fact that it is not anindividual component having a predetermined break point such as theH-profile piece 16 which is used for stabilizing the shape of the spigotmember 5, but rather, two completely separate components are used fromthe very beginning The omission of the predetermined break point 18 doesof course ease the task of tightening the bolts 6, but does not simplifythe assembly process overall due to the larger number of parts that haveto be handled. Moreover, as the irregularly serrated, mutually jammingcontours of the predetermined break point 18 are omitted, the feet 21must be of a somewhat greater material thickness than the web member 15in order to prevent the two feet 21 from being pushed above one anotherin the event of a collision.

The possibility of such a displacement above one another is excluded inthe embodiment of FIG. 9. Here, the spigot member 5 is reinforced by aT-shaped profile piece 23 and a plate-shaped profile piece 24, wherebythe foot 25 of the T-section profile 23 extends into the directproximity of the plate-shaped profile piece 24. However, due to thelarge length, larger deformation moments can occur on the foot 25 thanon the feet 21 of FIG. 8 so that here too, an increased materialthickness may be necessary in order to ensure sufficient form stability.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention, it being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims and their legal equivalents.

1. A frame structure for a motor vehicle, comprising: a longitudinalbeam; a bumper carrier; and a crashbox attaching the bumper carrier tothe longitudinal beam, the crashbox comprising: a section that iscompressible in a longitudinal direction, and a spigot subassemblyconfigured for attachment to the longitudinal beam, wherein the spigotsubassembly is configured for insertion into a cavity of thelongitudinal beam, wherein a support strut extends between two rigidside flanks of the spigot subassembly through an internal cavity of thespigot subassembly, and wherein the rigid side flanks of the spigotsubassembly are attached to opposite walls of a cavity of thelongitudinal beam and a predetermined break point is broken.
 2. A framestructure in accordance with claim 1, wherein the spigot subassembly isattached to the longitudinal beam by means of bolts that pass throughthe opposite walls of the longitudinal beam and the rigid side flanks ofthe spigot subassembly.
 3. The frame structure of claim 1, wherein thepredetermined break point is disposed on the support strut.
 4. The framestructure of claim 3, wherein the predetermined break point is disposedproximate one of the two rigid side flanks.
 5. The frame structure ofclaim 3, wherein the predetermined break point is centrally disposed onthe support strut.
 6. The frame structure of claim 3, wherein the brokenpredetermined break point divides the support strut into two portionsand wherein the two portions of the support strut are configured toengage one another in the event of a collision to inhibit movement ofthe two rigid side flanks towards one another.
 7. The frame structure ofclaim 6, wherein the two portions have substantially equal lengths in alateral direction of the motor vehicle.
 8. The frame structure of claim1, wherein a substantial portion of each of the rigid side flanks of thespigot subassembly is in direct contact with the opposite walls of thecavity of the longitudinal beam.
 9. The frame structure of claim 1,wherein the spigot subassembly comprises a sleeve having a cavity and apair of member pieces inserted into the cavity of the sleeve, eachmember piece of the pair of member pieces being attached to the sleeve,the support strut being broken into two strut portions, each strutportion being attached to a respective member piece, the two strutportions extending towards one another, and the two strut portionsconfigured to engage one another to inhibit the opposite walls of thecavity of the longitudinal beam from moving towards one another in theevent of a collision.
 10. The frame structure of claim 9, wherein thesleeve includes a corrugated slot to permit expansion of the sleeve in alateral direction of the motor vehicle when the sleeve is attached tothe longitudinal beam.
 11. The frame structure of claim 9, wherein thesleeve includes a pair of oppositely disposed corrugated slots to permitexpansion of the sleeve in a lateral direction of the motor vehicle whenthe sleeve is attached to the longitudinal beam.
 12. The frame structureof claim 9, wherein the sleeve defines a plurality of sleeve bolt holes,wherein the pair of member pieces defines a plurality of member boltholes, wherein the member bolt holes are configured to align with thesleeve bolt holes when the pair of member pieces is inserted into theinternal cavity of the sleeve, and wherein the member bolt holes areconfigured to engage bolts.